Half roll of tyvek supro. 1m x 25m. Save yourself some money if you don't need a full roll.

Dupont Tyvek Supro Roofing Membrane 1m.

The best product on the market. Lots and lots of tests verify how good this is. Just Google it.

DuPont Tyvek Supro is a durable, water resistant membrane that is reinforced with a laminated polypropylene nonwoven. This airtight, vapour-permeable membrane is extremely water-resistant, and can be used for all supported and unsupported pitched roofs.
Tyvek Supro does not need any soffit, tile or ridge ventilation, which can save time and money in the construction process. In addition to warm, hybrid and cold roofs, applications include Scottish sarking board systems, low-pitched metal roofs, and wall and floor applications.
Tyvek Supro water resistant membrane products are designed to withstand prolonged UV radiation and high temperatures, and come with full BBA and IAB approval for use in all pitched roof constructions.